1. Field of the Invention
The present invention relates to a contactless data carrier and a contactless data carrier system used for measuring physical quantities.
2. Description of the Related Art
Contactless data carriers (sometimes referred to as transponders) and interrogators (sometimes referred to as readers) are now widely employed for simple data processing purposes in situations in which the small size, light weight, and low cost of the contactless data carriers offer significant advantages. In addition, contactless data carriers equipped with sensors are beginning to find uses in measurement systems. Japanese Patent Application Publication No. 10-289297, for example, discloses a contactless data carrier equipped with a built-in temperature sensor and pressure sensor for monitoring temperature and pressure inside an automobile tire.
A number of problems, however, arise when a contactless data carriers are equipped with sensors. One problem is that the advantages of low cost, small size, and light weight are apt to be lost. Aside from the added size, weight, and cost of the sensor itself, there are the power requirements of the sensor and its associated signal-processing circuitry, typically including an analog-to-digital converter. If these requirements surpass the power that can be supplied from the energy of the interrogator signal, the contactless data carrier must have a battery, but batteries are neither inexpensive nor small nor light in weight.
Another problem is that the contactless data carrier is limited by its built-in sensor or sensors to making particular measurements. The contactless data carrier manufacturer must therefore manufacture different types of contactless data carriers for different measurement applications.
One way to minimize the number of different types of contactless data carriers is to equip each contactless data carrier with only one sensor, but then when several physical quantities need to be measured at the same location, several contactless data carriers must be installed. This is inconvenient, and the interrogator must communicate with each contactless data carrier separately, which takes time and requires extra power.
If a single contactless data carrier is equipped with a plurality of sensors, its size, weight, and manufacturing cost increase considerably, while the range of applications in which the contactless data carrier can be efficiently employed becomes limited to applications requiring a specific set of measurements. Production volumes of such multi-sensor contactless data carriers are therefore comparatively small, making the contactless data carriers even more expensive to manufacture.
Moreover, there are practical limits on the number of built-in sensors that a contactless data carrier can have. Even putting two sensors into a contactless data carrier is often difficult.
There is accordingly a need for a small, lightweight, and inexpensive contactless data carrier that is adaptable to multiple types of measurements and can accommodate multiple sensors, for an interrogator that can take measurement data from this type of contactless data carrier, and for the associated system software and operating methods.